USB base



FIG. 1 is a top, front and right side perspective view of a USB base, showing my new design;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a right side elevation view thereof; the left side elevation view is a mirror image thereto;

FIG. 4 is a back elevation view thereof;

FIG. 5 is a top plan view thereof; and,

FIG. 6 is a bottom plan view thereof.

The broken line showing of the environment is for illustrative purposes only and forms no part of the claimed design. 

The ornamental design for a USB base, as shown and described. 